1. Technical Field
The present invention relates to a method for producing a group III nitride semiconductor light-emitting device including the step of removing a growth substrate by a substrate lift-off process, and a group III nitride semiconductor light-emitting device produced thereby.
2. Description of Related Art
A sapphire substrate is generally used as a growth substrate of a group III nitride semiconductor. However, sapphire has problems with respect to electrical conductivity and thermal conductivity, and has no clear cleavage surface, so that processing thereof is not easy. Accordingly, as techniques for solving these problems, there have been developed techniques (substrate lift-off) of allowing the group III nitride semiconductor to grow on the growth substrate, and then, removing the growth substrate.
One of the techniques is a laser lift-off process. This is a process of joining the group III nitride semiconductor layer to a support substrate, and then, irradiating an interface between the growth substrate and the group III nitride semiconductor with a laser beam to decompose the group III nitride semiconductor layer, thereby separating and removing the growth substrate. Further, as another technique, there has also been known a process of introducing a chemical solution soluble layer as a layer close to the growth substrate of the group III nitride semiconductor layer, joining the group III nitride semiconductor layer to a support substrate, and then, dissolving the above-mentioned chemical solution soluble layer with a desired chemical solution, thereby removing the growth substrate (chemical lift-off process).
When the laser lift-off process is applied to the preparation of a light-emitting device, since the group III nitride semiconductor layer has a structure of an n-type layer, an active layer and a p-type layer from the growth substrate side, a surface of the group III nitride semiconductor layer becomes a surface of the n-type layer. In the related-art structure, a fine concavo-convex processing is performed by wet etching on a surface of the n-type layer which is exposed by the removal of this growth substrate, in order to enhance the light taking-out efficiency. However, there are variations in the concavo-convex processing by wet etching, and flat regions and unevenness regions having a depth not effective for the light taking-out efficiency remain in places. Further, unevenness is formed in six-sided pyramid form in which side surfaces equally have an angle of about 60 degrees. Furthermore, the distance between the convex portions is narrow, so that light once emitted outside from the convex portion enters again the inside of the n-type layer from the convex portion in some cases. For these reasons, the light taking-out efficiency has not been able to be sufficiently enhanced only by forming fine unevenness.
JP-A-2008-47861 shows a method for improving the light taking-out efficiency by performing a two-step concavo-convex processing. Specifically, concave portions having a grid pattern are formed on an exposed surface of the n-type layer by etching using a mask, and then, fine unevenness is formed on the surface of the n-type layer and bottom surfaces of the concave portions by wet etching.